2,665,317 United States Patent Office
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Patented Jan. 5, 1954 2,665,317 UNITED STATES PATENT OFFICE 2,665,317. METHOD OF TREATING RUBBER OBTAINED FROM RUBBER-BEARING PLANTS Frederick E. Clark and Irvin C. Feustel, Salinas, Calif., assignors to the United States of America as represented by the Secretary of Agriculture. No Drawing. Application November 14, 1951, Serial No. 256,356 4. Claims. (CI. 260-818) (Granted under Title 35, U. S. Code (1952), sec. 266). 1. 2 A non-exclusive, irrevocable, royalty-free The resulting product is the crude resinous license in the invention herein described, for all guayule rubber of commerce. It contains an governmental purposes, throughout the World, average of about 20-25%, resin (acetone or alco with the power to grant sublicenses, for Such pur. hol. Soluble constituents). This gross impurity poses, is hereby granted to the Government of limits the usefulness of guayule rubber and for the United States of America. this reason efforts are being made to develop a This invention relates to a method for treating deresination process by means of which a crude natural rubber extracted from various shrubs, rubber of superior quality can ultimately be pro wines, and other plants for the purpose of pre duced. venting clumping or cohesion of rubber particles 0. The Wet rubber worms, as recovered from the during handling and processing. The method scrub milling, operations are roughly comparable is specifically applicable to rubber obtained from in size to grains of rice and they possess a micro the guayule shrub (Parthenium. argentatun, Sponge-like structure. At this point in the proc Gray), one of the most promising sources of nati ess the Worms are regarded as being generally ural rubber that can be grown in the United best suited for deresination by solvent extraction states, in which connection it will be described because of their favorable size, granular condi in detail. tion, and pervious structure. Hence, efforts are In the recovery of rubber from guayule by the being, made to develop a deresination process conventional mechanical extraction process, the based on the use of wet scrub-milled worms. At harvested shrub is first defoliated, comminuted, 20 and crushed. This material is then milled in a times, however, the worms clump or cohere to water slurry with pebbles in a pebble. mill until form relatively, large and impervious aggregates the rubber is completely released from plant or maSses which cannot be eXtracted because the resin solvent will not penetrate the lumps that cells and agglomerated into macroscopic particles have been formed. Clumping may take place to or granules commonly called "worms.” The 25 varying degrees at any stage in the pebble mill pebble-milled slurry is then discharged into a ing process although operational difficulties due flotation tank wherein additional water is added to clumping. have principally been focused on the and the mixture thoroughly stirred to facilitate Scrub; milling step since this is the most critical separation of the worms from the plate-material one from the standpoint of applying corrective (bagasse). After standing for a short period, the 30 treatments for worms already clumped and for rubber worms, float to the surface of the Water attaining a Well dispersed or non-cohering con while the bagasse sinks. The Worms are recov dition in which the worms are suitable for drying ered by skimming the flotation tank. The Worms or for resin extraction. are then given a hydrostatic. pressure treatment It is frequently very difficult and at times im in hot water at 500 p.s. i. or greater, to water 3. possible, to break up all the clumps or to prevent log cork fragments which floated with the rub further clumping in the scrub mill. Sometimes ber in the first flotation. After this pressure the lumps or aggregates of worms become so treatment the worms are given a second flotation, large, as to weigh. Several pounds. Clumped similar to the first. The waterlogged cork frag rubber is not only impossible to deresinate effec ments now sink and the Worms are again. 40 tively; but is also unsuitable for drying because skimmed from the flotation tank. The Worms the normal-sized Worms in the mixture become are next subjected to a scrubmilling treatment, Over-dried and degraded by the prolonged heat This constitutes pebble milling of a slurry of the ingnecessary to dry, the lumps. worms in hot water, followed by a third flotation It is necessary to keep the Worms submerged for final purification from adhering or imbedded 45 in Water if there is a break in processing con plant fibers. The quantity of Water used for tinuity or a delay in transport from one proc scrub milling is usually about 20 parts to 1 of essing step to another in order to minimize rubber (dry basis). The ratio of Water to rubber clumping and also to protect the rubber from ex in the flotation tank is about 100 to 1. The Wors posure to air. Since it is very susceptible to oxida skimmed from the third flotation are usually 50 tion, unless an antioxidant has been applied. spread out on trays and dried in a vacuum drier. However, if worms are held in a container for 2,665,817 3. 4. more than a few hours a closely cohering maSS any of the materials known to have the ability of rubber is usually formed which requires con to disperse insoluble materials in aqueous media, siderable effort to break up into individual Worms. Thus for example One may use polyoxyethylene Steam treatment is often resorted to in such sorbitan monolaurate; polyoxyethylene lauryl cases but at best this has only a temporary bene alcohol; dialkyl esters of Sulphosuccinic acid ficial effect. such as dihexyl sodium Sulphosuccinate, dioctyl The rubber possesses some tackiness and con sodium sulphosuccinate; the sodium salt of de sequently there is a natural tendency for a mass hydrogenated roSin; Sulphated higher alcohols of worms to cohere especially under conditions such as sodium dodecyl sulphate, Sodium tetra where the pressure resulting from its own weight decyl sulphate, sodium hexadecyl Sulphate; al becomes appreciable and the period of contact kylated aromatic Sulphonates Such as Sodium is prolonged. decyl benzene sulphonate, sodium dodecyl ben In some cases a high degree of clumping is zene sulphonate, sodium tri(isobutyl) benzene caused by a rapid cooling of the water or other sulphonate, Sodium alkylated (C12 to C18) ben liquid in which the worms are being processed or 5 Zene Sulphonate, etc. The insoluble Soap in the colntained. In other cases clumping is associated dispersion may of course be derived from any of with certain physiological influences of the shrub the metals and fatty acids, or mixtures, referred from which the rubber is milled since the difficul to above. ties are more pronounced during the shrub Instead of applying the pre-formed insoluble flowering season. Also, rubber milled from young 20 Soap to the rubber particles, the in Soluble Soap shrub has a greater tendency to clump than rub may be formed in situ on the rubber particles or ber from old shrub. in the coating bath by interaction of (1) a The object of this invention is to treat the higher fatty acid or water-soluble salt thereof worms in such a manner as to prevent clumping With (2) a Salt of a metal Which forms Water or cohesion of the individual Worms. A further 25 insoluble soaps. Thus specific methods of form object is to provide a treatment which will re ing the insoluble Soap coating on the rubber par tain its effectvieness not only with regard to han ticles are as follows dling of the worms prior to deresination but also (a) Interaction of a higher fatty acid such as during deresination and/or in preparation of the stearic acid with a Water-Soluble Salt of a metal rubber for drying. 30 which forms water-insoluble soaps, as for ex We have found that the above objects can be ample, calcium chloride, zinc chloride, or other attained by coating the worms with a thin film Water-soluble SaltS of the metals previously re of a water-insoluble metallic Soap, that is, a ferred to. water-insoluble salt of a metal and a higher fatty (b) In the above technique (d), the fatty acid acid. The insoluble soap film prevents the Worms 35 may be replaced by a Water-soluble salt thereof from clumping during handling or processing of Such as an alkali metal salt. Thus one could use the worms as in the various milling, flotation, and for example Sodium stearate or an Ordinary soap hydrostatic pressure operations. Moreover, the Which consists of the sodium salts of a mixture of insoluble soap-coated worms will not clump even higher fatty acids. if held en masse for a prolonged period of time. (c) Interaction of a higher fatty acid such as Furthermore, the film does not prevent moisture stearic acid with the metallic ions such as cal vapor from passing off readily during drying nor cium and/or magnesium contained in hard water does it prevent penetration of a Solvent such as in which the rubber is processed. acetone during deresination. Still further, the (d) In the above technique (c), the fatty acid insoluble soap film does not have any adverse is replaced by a water-soluble fatty acid salt such effect on the quality of the rubber. as Sodium stearate or ordinary soap. The insoluble soap may be derived from many In applying the procedures outlined above the different materials. Thus, the metal moiety of rubber worms may be first contacted with a solu the insoluble soap may be any metal which forms tion or dispersion of the fatty acid (or water an insoluble soap, as for example, zinc, cadmium, Soluble Salt of a fatty acid) and then contacted aluminum, magnesium, lead, calcium, strontium, With a Solution of the insoluble soap-forming barium, tin, mercury, and so forth.